Valves
In the closed position, the dome sits concentrically beneath the inlet port below which the inflatable seal assembly is positioned. The inflatable seal, which is a complete ring of an elastomer or rubber approximately 25mm wide, covers the periphery of the dome. A controlled gap of about 1 mm between the face of the dome and the face of the inflatable seal (seat) allows the dome to rotate into and away from the closed position. Particles from the media entering the valve are allowed to pass or remain between the seal and the surface of the dome. Closing the Inflatek Valve automatically sequences the seal to inflate by initiating a limit switch when the dome drive shaft completes a 90° rotation to the closed position. Seal inflation is achieved by introducing compressed air or other gas through a small plenum behind the sealing ring. With sealing air pressures of 1.7 bar or 20% higher than the pressure differential across the valve closing member are applied, the seal inflates and engages the periphery of the dome component. Small particles that enter the gap between the seal face and the dome surface are entrapped by the expanding face of the rubber seal to prevent their movement and subsequent wear to the seat. This technique of entrapping particles between the seat and seal has been proven to considerably reduce valve seat wear even when performing with the fine abrasive powders such as ground glass and coke breeze.
The pneumatic seal and its operating action provides and additional benefit: As wear does occur on the seal face or the dome component, the expanding seal provides wear compensation automatically until a wear limit is reached. The wear limit is considerably greater than any other valve design. The pneumatic seal or inflatable seat is a masterpiece of simple mechanical design. The seal component is a continuous ring with a special profile that provides both correct location and effective anchoring. There are no special fasteners or adhesives to complicate the process of assembly or replacement. The seal ring is beneath the top plate of the valve so that when the valve is used in its preferred direction of flow mode, the seal is completely protected from the flow of media through the valve. The manufacturer has developed an impressive array of seal materials utilising various rubber compounds and elastomers to insure temperature and chemical compatibility with media passing through the valve.
One of the most impressive innovations of this remarkable valve is the use of water for cooling purposes in high- temperature applications. It was originally regarded by the valve designers to be a disadvantage to require an additional utility to the valve to enable its operation for high temperature duties. However, the choice between exotic materials of construction with experimental polymers for the seal over the addition of cooling channels and additional utility connections has proven to be a wise and effective choice enabling a simple, effective and low-cost valve solution for some of the most demanding applications in industry. Two temperature design steps are offered to ensure economic targeting of the product. For service up to 280°C, the valve is provided with a water-cooling channel around the pneumatic seal area with in the top plate. For service up to 350°C, the addition of a water-cooled dome component is provided. The cooling water is introduced through a channel in one shaft axis to the supporting leg of the some, through the dome chamber and exiting the valve in the same manner through the opposite shaft
42 Solids & Bulk Handling • November 2010
50mm Inflatek Valve
– an unusual but effective solution. The Inflatek Valve is widely used in such high-temperature applications as ash handling for utilities and industrial coal-fired boiler plants, as well as many high-temperature chemical processes. Valve operation is also versatile. The simple rotational actuation has allowed many types of valve operators to be applied, from the standard air actuation to hydraulic and even manual hand operation. This versatility has allowed the valve to be used in applications to solve special problems such as: • Flow regulation by positioning the dome closing member as required by modulated signal from down-stream processes in addition to the standard closing and sealing function. • Snap-open action to minimise gas velocities through the valve when operating with high-pressure exhaust applications, again, in addition to the standard closing and sealing function.
Application diversity
The application capability of the basic valve design is unusually wide for many reasons as explained in the design discussion. These are summarised as follows: Abrasive media: Abrasive slurries, bulk powders, granules and dust-laden gases can cause rapid seat erosion and ineffective closure in conventional hard seat valve designs. The inflatable seat and its automatic wear compensation feature overcomes these problems associated with abrasive media. Pressure differential: Also causes accelerated seat wear in conventional valve designs, even though hardened seats may be used. Pressure differential causes un-trapped particles in hard seat valves to move across the seat at high velocity which erodes hard seats and commences the wear process. The inflatable seal effectively entraps the particles and prevents particle movement and, therefore, wear. High temperature: Thermal expansion prevents consistent valve seat action in hard seat valves. The inflatable seal provides seal action compensation throughout the temperature range. Valve performance on media temperature up to 350°C has been achieved.
Close and seal: The displacement and cutting action of the dome component and its spherical shape rotating within the valve housing allows closure through a solid column of bulk materials, followed by the seat sealing action of the inflatable seal. For more information contact MacTenn on tel: 01787 882 422 or visit:
www.mactenn.com
www.solidsandbulk.co.uk
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